The structure of perceived pain. The objective is the development of a representation system for specification of the perceptual or experiential characteristics of pain. Varieties of pain will be specified by over 100 wards frequently used as descriptors by individuals in pain. Judgments of relative degree of similarity of pairs of pains so defined will be obtained through a series of experiments employing overlapping subsets of these descriptors. The multidimensional analysis approach will be used to obtain a spatial representation of both quality and intensity of perceived pain. Preliminary results indicate that pain quality is best represented by the ideal-type model, which requires use of a hyperspherical spatial model. Methods will be developed to solve for location of points within a right hyperspherical triangle when given only empirical estimates of the mutual interpoint distances in arbitrary units. Clustering of patients presenting pain into homogeneous subsets. The increase in number of pain clinics will be accompanied by rapid accumulation of data files for pain patients that include much more information on variables considered important by specialists in a variety of different fields. Methods are needed for discovering subsets of patients that are homogeneous with respect to known subsets of variables. Clustering procedures of a patient by variable matrix into homogeneous submatrices are proposed. The aim is to develop clustering algorithms for each model. Homogeneous groups thus obtained would be of great value in evaluation of effectiveness in managing pain of both drug agents and also the various surgical, psychological, and physical treatment procedures.